The quest for highly sensitive and stable X-ray detectors has intensified, driven by diverse applications such as medical diagnostics and industrial inspection. Recent strides have been made in harnessing the potential of lead halide perovskites for radiation detection, thanks to their remarkable optoelectronic properties. However, the toxicity of Pb and intrinsic material instability restrict their practical applications as next-generation efficient detectors. Here, we have developed environment-friendly three-dimensional (3D) bismuth-chloride perovskites designed for highly sensitive and stable X-ray direct detection. By the introduction of monovalent Na